Focused electromechanical device



Aug. 21, 1951 A. w. WILLIAMS FOCUSED ELECTROMECHANICAL DEVICE 3 Sheets-Sheet 1 Filed April 21, 1949 SOURCE OF' AN ACOUST ICAL DISTURBANCE AMPLIFIER INVENTOR. ALFRED L.W. WILLIAMS AMPLIFIER 0 AND IMPEDANCE ULTRASONIC- FREQUENCY 1 ATCHING UNI SIGNAL GENERATOR ATTORNEY Aug. 21, 1951 A. w. WILLIAMS FOCUSED ELECTROMECHANICAL DEVICE 3 Sheets-Sheet 2 Filed April 21, 1949 FINE SOLID FR EQU ENCY SIGNAL SOURCE ULTRASONIC- VESSEL LIQUID AG TATOIR ULTRASONIC c TREATMENT DEVICE DISPERSION STORAGE FIG. 3

INVENTOR. ALFRED L.W. WILLIAMS ATTORN EY 1951 A. L. w. WILLIAMS FOCUSED ELECTROMECHANICAL DEVICE 3 Sheets-Sheet 3 Filed April 21, 1949 Fur: m M W 5:25 3 3 5 m I flos' INVENTOR. ALFRED L.W. WILLIAMS ATTORNEY Patented Aug. 21, 1951 FOCUSED ELECTROMECHANICAL DEVICE Alfred L. W. Williams, Cleveland Heights, Ohio, assignoi' to The Brush Development Company, Cleveland, Ohio, a corporation of Ohio Application April 21, 1949, Serial No. 88,865

19 Claims. 1

This invention relates to electromechanical devices of the type which operate in association with an acoustical medium and, more particularly, to a focused electromechanical device for transduclng between two types of energy, one type of which is mechanical energy in an acoustical medium at a focal region of the device and the other type of which is electrical energy translated by electrodes thereof. The phrase mechanical energy, as used in this specification and in the appended claims, embraces and includes the phenomena of acoustical propagation of energy through any material medium, so that acoustical energy is considered as being one form or manifestation of mechanical energy.

This application is a continuation-in-part of 2 center, depending on response in the Y-direction or the Z-direction has the greater effect. To compensate for these variations concave radiating bodies of quartz have been devised in which the thickness dimension varies from point to point in accordance with a complicated formula. Even with these precautions the radius of curvature of the spherical surfacemust be made quite large and the angle from the center of curvature subtended .by opposite edges of the concave surface must be made quite small to obtain satisfactory operation.

my application Serial No. 767,987, filed August 11,

1947, and assigned tov the same assignee as the present invention, and also is a continuation-inquartz radiator may be fashioned from a relatively large single crystal of quartz so that the crystallographic X-axis is normal to the radiating surface at the center of the concave surface.

A concave quartz acoustical radiator'made in this way has the disadvantage that the X-axis is normal to the radiating surface only at its center. As a result, the peripheral areas of the surface have components of motion tangentially of these areas. Not only do these tangential components of motion contribute nothing to the acoustical radiation, but the components of motion normal to the surface lack sufficient amplitudes to make their full contribution to the focused radiation. Moreover, the frequency constant varies from point to point in the portions of the quartz adjacent to various surface areas of the radiator, so that it is very diflicult to obtain the desired motion of the radiating surface as a whole. Not only do the above-mentioned properties of the material vary as the direction of the X-axis departs from the normal direction, but the extent and nature of such variation at a given distance from the center of the concave surface are different in different transverse directions from the 55 walls of polycrystalline dielectric material such Another method of overcoming the difiiculties electric elements with plane surfaces into a composite transducing device in which each of these elements serves as one elemental portion of a concave surface. This-has the advantage of requiring only relatively small pieces of transducer grade quartz, since the larger pieces, suitable for the production of a single focused transducer body large enough-to effect the transfer of useful amounts of energy to or from an acoustical medium, are rare and expensive. However, the design and fabrication of multi-element trans- .ducers also is expensive, and the finished transducers are more subject to failure due to such causes as improper cementing of the numerous elements and breakage of electrical leads. The more complicated multi-element construction results in some of the concave surfacebeing inactive and is obviously less satisfactory than a unitary construction as regards both efficiency and tenance.

It has been observed that certain materials of a ceramic nature are capable of substantial electromechanical response. This response is realized to best advantage when the material is treated electrically to establish acondition of electrostatic polarization therein. Polycrystalline materials which exhibit this unusual response include certain titanates of the alkaline earth metals, notably barium titanate, Bodies of such polycrystalline materials, polarized to develop a substantial linear electromechanical response, are disclosed and claimed in the copending application Serial No. 740,460, filed April 9, 1947, in the name of Hans Jafie and assignedto the same assignee as the present invention.

In my aforesaid copending application Serial No. 767,987 there is disclosed and claimed as an electromechanical transducer comprising a hollow shape such as a cylinder or a spherehavingwhether the piezoelectric main- 7 as barium titanate. The inside surfaces of the cylinder or sphere may be in acoustical contact with a medium capable of transmitting hydrostatic pressure for translation of acoustical energy between those surfaces and the medium. Electrodes are provided on the inside and outside surfaces, and a source of a unidirectional potential is shown coupled across these electrodes so as to provide a polarizing field acting in the thickness direction on the walls of the hollow shape. Such an arrangement is illustrated, for example, in Fig. 1 of the drawing in the aforesaid application, in which a cylindrical container filled with a liquid is shown with a piston extending from a diaphragm in contact with the external air through an end wall axially into the container to act upon the fluid therein. In my aforesaid application Serial No. 32,593 there is disclosed and claimed an electromechanical transducer comprising a body of such a polycrystalline dielectric material having wall portions surrounding a region which has a medial line extending generally longitudinally of these wall portions. This body may have the shape of a straight cylindrical tube in which the medial line is the axis of the tube. The inside and outside walls of the tube are provided with electrode means. This tubular apparatus is further provided with mechanical means such that motion of the mechanical means is associated with bending of the medial line.

I have discovered that electromechanically responsive polycrystalline material, such as .barium titanate, formed into a body having a concave surface, such as a spherical or cylindrical surface, may be arranged to provide a focused electromechanical device for efiecting electromechanical coupling with an acoustical medium in which the useful acoustical energy is concentrated in a more or less limited focal region relative to the body of dielectric material.

It is an object of this invention, therefore, to provide a new and improved focused electromechanical device which substantially avoids one or more of the limitations and disadvantages of prior arrangements of the type described.

It is another object of the invention to provide a new and improved focused electromechanical device which may be constructed easily using relatively inexpensive and easily available materials.

It is a further object of the invention to provide an improved electromechanical focusing device of sturdy construction which is not sub- Ject to the complexity of structure or to the tendency toward breakage of the prior arrangements.

It is a still further object of the invention to provide an electromechanical device exhibiting a high order of response during transducing between mechanical energy in an acoustical medium at a focal region of the device and electrical energy translated by electrodes thereof.

It is an additional object of the invention to provide a new and improved focused electromechanical device having both a large radiating or receiving surface and a small focal length.

It is yet another object of the invention to provide an electromechanical device in which acoustical energy at a focal region of the device is collimated into generally parallel rays of acoustical energy which may be caused to propagate in a region which is elongated but of small crosssectional area relative to the surface area of the radiator of the focused energy.

In accordance with an embodiment of the invention, a focused electromechanical device for transducing between two types of energy, one type of which is mechanical energy in an acoustical medium at a focal region of the device and the other type of which is electrical energy translated by electrodes associated with the device, comprises a body of electromechanically responsive polycrystalline dielectric material having a concave major surface, determining a mechanical-energy-translating location at a focal region in front of the concave surface, and electrically polarized to provide a major electromechanical response in a thickness mode of motion normal to the concave surface. The device also comprises electrode means, including electrodes individually disposed adjacent to the aforesaid concave surface and to the opposing surface of the body, and including electrical terminal means coupled to these electrodes to establish an electrical-energy-translating location. The device also includes means for applying energy of one of the two aforementioned types to the corresponding one of the energy-translating locations and for utilizing energy of the other of these types developed at the other of the energy-translating locations.

In accordance with a particular feature of the invention, a focused electromechanical device includes a volume of an acoustical medium in effective acoustical contact with the concave surface and extending toward the focal region. There also is provided means, disposed near the focal region in effective acoustical contact with this acoustical medium and including a surface effective to change the curvature of an acoustical wave front, for converting between acoustical energy which propagates in non-parallel paths in the regions between the concave surface and the last-mentioned means and related acoustical energy which propagates in generally parallel paths in an elongated mechanical-energy-translating location. It will be observed that the mechanical energy, in accordance with this feature of the invention, is directly applied or directly utilized in an elongated energy-translating location more or less remote from the focal region of the device; nevertheless, the mechanical energy is propagated in the form of acoustical energy past the above-mentioned means disposed near the focal region, so that the focal region still remains a mechanical-energy-translating location, to which mechanical energy is applied acoustically from the elongated location or in which mechanical energy is utilized by causing it to be propagated acoustically in collimated form into the elongated location.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

In the drawings. Fig. 1 is a cross-sectional view, partly schematic, of a device in accordance with the invention for transducing from mechanical energy to electrical energy; Fig. 2 is a crosssectional view, also partly schematic and omitting supporting structures, of a device in accordance with the invention for transducing from electrical energy to mechanical energy; Fig. 3 is a block diagram' of a complete apparatus for dispersing a finely divided solid in a liquid medium; Fig. 4 is a sectionalized perspective view of a portion of the arrangement illustrated in Fig. 3 which embodies the present invention;

. Fig. 5 is a perspective view'of another embodiment of the invention; and Figs. 6 and! are cross-sectional elevations of two alternative.

forms of a device embodying a particular fcature of the invention.

Referring to Fig. 1 of the drawings, there is of which is electrical energy translated by electrodes thereof. More particularly, there is illustrated in Fig. 1 a device for transducing from mechanical energy to electrical energy. The mechanical energy is introduced into the device at a small source of such energy. This source of an acoustical disturbance, occupying a rather small volume of space, is designated schematically in Fig. l as a small volume-indicated at the reference numeral II. This source II is immersed in an acoustical medium, for example a liquid body of water or oil. The source ll may be, for example, a small acoustical radiator whose response it is desired to test with high sensitivity of the testing mechanism and with a minimum of interfering radiation from regions outside the focal region of the testing device.

The device illustrated in Fig. 1 is viewed in cross section, the section being taken centrally through the parts of the device which are not shown purely schematically, and comprises a body l2 of electromechanically responsive polycrystalline dielectric material. Preferably this dielectric material is a titanate material of the type which, upon treatment with a unidirectional electrical field, becomes electrically polarized so as to provide a very substantial linear electromechanical response. The body l2 of such a titanate-type material advantageously is of a polycrystalline dielectric material composed primarily of barium titanate. This body has a concave major surface l3 approximately coinciding with a substantial portion of a hypothetical spherical surface. Thus, the surface l3 of the body l2 may be thought of as a portion of the inside surface of a hollow sphere of dielectric material, and the boundary of the spherical surface is a circular line formed by the intersection with the sphere of a hypothetical plane, seen edgewise in Fig. 1 as a line l4, It. The body I2 is provided with a flanged portion l6, IS the front surface of which lies in the-plane l4, I4. The concave spherical surface l3 determines a mechanical-energy-translating location at a focal region in front of the concave surface. More specifically, this mechanicalrenergy-translating location coincides with the focal region in the neighborhood of the center of the hypothetical spherical surface, with a portion of which hypothetical surface the concave surface l3 approximately coincides. As illustrated in Fig. 1, the source ii is placed approximately at the center of curvature of the spherical surface, although it will be understood that the focal region may occupy a substantial volume in the neighborhood of the central point due to dispersion effects and to imperfections in the geometry of the concave surface l3. In fact, a very substantial focusing action may be obtained with bodies having concave surfaces deviating quite materially from a geometrical shape affording ideal focusing action.

The body of dielectric material I2 is electrically polarized to provide a major electromechanical response in a thickness mode of motion normal to the concave surface l3. While this condition of polarization may be provided by applying a constant unidirectional electrical voltage in the thickness direction across the body 12. for example, by the use of polarizing equipment such as that described in the aforesaid copending application Serial No. 740,460, the method of pro-,

viding such polarization is not limited to such an application of a biasing voltage. Thus, a high unidirectional voltage, which may be a voltage approaching the breakdown voltage for the thickness of the material, may be applied for only a short period of time to induce a condition of remanent electrostatic polarization sufficient cave surface.

to provide the desired high electromechanical response. l2 have a generally uniform thickness between the concave surface l3 and the convex opposing I surface H in the directions normal to the con- As mentioned hereinabove, the body has a major electromechanical response in a thickness mode of motion by virtue of the electrical polarization thereof. Since the polarized condition is brought about by polarizing voltage applied in the'thickness direction, that is, between the concave surface I3 and the opposing surface II, it will appear that the body i2 is polarized in directions differing at various portions of the body and everywhere substantially normal to the concave surface thereof.

Although the dielectric bodies of the devices of the present invention may be supported so that they are practically entirely surrounded by an acoustical medium, increased eiliciency usually may be derived by isolating the opposing or back surface I! of the body l2 from the medium, so that only the concave urface I3 is in effective acoustical contact with the medium. Accordingly, in the Fig. l arrangement the body i2 is provided with a container l8 of an electrically conductive material such that any fluid which might occupy the spaces inside the container does not serve as a conductor of acoustical energy between the back surface I1 and the acoustical medium in which the container l8 and the source Ii are immersed. The container I! has a'circular opening, to the inside edges of which the front surface of the flange I6 is cemented.- The body I2 is provided with electrode means, including electrodes i9 and 20 individually disposed adjacent to the concave surface l3 and to the opposing surface I! respectively of the body l2. It is convenient-to extend the front electrode l9 somewhat beyond the boundary I4, M of the spherical surface l3 so as to make electrical contact with the edge of the circular opening in the container it. A supporting block 2| is fastened within the container It to the back of the container, and a, thick retaining sheet 22 of a resilient material is compressed between the support 2i and the electroded back surface 11 of the body l2. The resilient sheet 22 is a nonconductor of acoustical energy, and may be made of rubber interspersed with numerous air cells which serve to decouple the back surface I! acoustically from they support 2!.

Electrical connections to the electroded body i2 are made in the Fig. 1 arrangement by means of a coaxial cable 23 having a metallic outer 'conductor 24 and an inner conductor 26, 26. The inner conductor 26 is spaced from outer conductor 24 by means of suitable center insulators such as, the insulators 21 and 28 illustrated at the two ends of the cable 23. If desired, the cable 23 may be supplied with a flexible, fluid-tight,

It is desirable that the dielectric body insulating covering, not shown, which may be cemented to the outside of the container I8 at the bushing where the cable passes through the wall of the container. The inner conductor 26 extends into the container and is soldered to the back electrode 20. At the remote end of the cable 23 the inner conductor 26 is connected to an electrical terminal 3|. The outer conductor 24, which is connected conductively to the metallic container I8 and thence to the front electrode I9, is connected to another electrical terminal 32. Thus the eiectrode means of the Fig. 1 device effectively includes the electrical terminal means 3|, 32 coupled to the electrodes 20, I3 to establish an electrical-energy-translating location, at the terminals and the associated electrical connections. Through this electrical-energytranslating location may pass the electrical currents associated with the transducing between electrical and mechanical energy during the operation of the device.

The device shown in Fig. 1 includes means for applying energy of one of the two types, namely, mechanical energy in an acoustical medium or electrical energy, to the corresponding one of the two energy-translating locations, namely, the mechanical-energy-translating location at the focal region or the electrical-energy-translating location at the terminals 3|, 32 and associated connections, and for utilizing energy of the other of these types developed at the other of these energy-translating locations. This means includes a volume of the acoustical medium mentioned hereinabove, which is in effective acoustical contact with the concave electroded surface I3 and extends toward the focal region. The same acoustical medium also occupies the focal region, although the mediumat or near the focal region may be a different acoustical medium, which in such case is in acoustical contact with the aforesaid volume of acoustical medium at an interface between the two media. In a preferred form of the device, however, the medium at the focal region is an extension of the above-mentioned volume of an acoustical medium, so that this medium not only is in acoustical contact with the concave surface I3 but also embraces the focalregion. In the Fig. 1 arragenment it is assumed that the entire container I8 as well as the regions between the surface I3 and the focal region is immersed in this medium. To avoid confusion in the drawings the acoustical medium has not been indicated in Fig. 1, it being understood that a fluid body surrounds the entire device except possibly for the remote end of the cable 23 and the electrical equipment connected thereto.

In the Fig. 1 arrangement the means for applying energy of one type and for utilizing energy of the other type may be considered as made up of two means, one being means for applying mechanical energy to the focal region to effect acoustical propagation of the mechanical energy through the aforesaid volume of the acoustical medium to the electroded concave surface I3 of the dielectric body I2, and the other being means including the electrodes l9 and 20 for utilizing the resulting electrical energy developed in the dielectric material of the body I2. The means for applying mechanical energy thus may include the source II of an acoustical disturbance as well as the portions of the acoustical medium embracing the focal region. The means for utilizing the electrical energy developed during transducing includes not only the electrodes l3 and fl but also an amplifier 33 having an input 8 circuit coupled to the terminals 3|, 32 and an output circuit coupled to a loudspeaker 34.

Considering the operation of the device shown in Fig. 1, an acoustical disturbance originates at the source II in a manner such as is described hereinabove. It may be assumed that this acoustical disturbance is the result of a mechanical motion or vibration of a solid body or area II, giving rise to an acoustical wave disturbance which propagates in the acoustical medium in all directions or at least in directions generally toward the electroded surface I3. Thus during the application of mechanical energy to the device a form of energy-transducing occurs at the surfaces of the source II, the mechanical energy of vibratory motion of these surfaces being changed into another form of mechanical energy, namely acoustical energy Propagating through the acoustical medium in which the device is immersed. An acoustical wave front propagating from the small source II reaches all points of the surface I3 at practically the same time, or, stated differently, the acoustical energy is, practically speaking, in phase at all points on the surface I3. This condition obtains for a source I I of an acoustical disturbance which occupies only the focal region determined by the shape of the surface I3, and is based on the fact that the spherical surface I3 is practically concentric with the spherical wave front originating at the small source II. It will be recognized by those skilled in the acoustical arts that this focusing action may be utilized to facilitate investigation of a condition of acoustical disturbance located essentially in the rather small focal region, rovided the frequency components associated with the acoustical disturbance are sufliciently high. If such components are so low in frequency that the corresponding acoustical wave lengths become roughly commensurate with the dimensions of the apparatus involved, the phase relationships necessary for effective acoustical focusing become degraded in a well recognized manner, and the practical advantages of the focusing action of the concave surface may be lost.

The acoustical energy impinging on the electrical surface I3 causes the body I2 to move or deform mechanically in a thickness mode of motion normal to the concave surface I3. Thus a densification or high pressure wave front in the acoustical medium in contact with the electroded surface I3 causes a monetary slight decrease in the thickness dimension of the body I2, while a subsequent rarefaction or low pressure wave front in the medium adjacent to the surface I3 causes a corresponding increase in this thickness dimension. Since the material of the body I2 is polarized in the thickness direction, this thickness mode of motion gives rise to a corresponding linear electrical effect, which may be manifested as an electrical field in the thickness direction causing a signal voltage to appear across the electrodes I9. 20 or as an electrical charge appearing on the electrodes. The electrical energy, repre-' sented by this voltage or charge translated by the electrodes I9, 20 of the Fig. 1 device, is translated further through the conductors 24, 26 and the- I is largely schematic and all supporting brackets have been omitted from the drawing. The device, with the exception of the associated electrical generator and amplifier equipment, may be assumed to be immersed in a fluid ac ustical medium which, however,-is not repres "Ydin the drawing. The focal region in the arrangement is a region in the neighborhood of a point 4|. This point 4| is the approximate center of curvature of two concave surfaces '42zand 43. These concave surfaces are similar 'to the surface l3 of the Fig. 1 device, but th major chord of each surface 42 and 43 subtends a greater angle at the point 4| than the angle subtended by a major chord of the surface l3. For a given major chord dimension the subtended angle conveniently is made greater in the Fig. 2 arrangement because th point 4|, where mechanical energy is to be developed, may be located in a practical apparatus quite close to the surfaces 42 and 43. The concave spherical surfaces 42 and 43 are surfaces of respective dielectric bodies 44 and 45, shown in cross section taken through a central plane, having respective back surfaces 46 and 41 opposing the respective concave surfaces 42 and 43. The body 44 is provided with electrodes 48 and49 adjacent to the surfaces 42 and 46 respectively, while the body 45 likewise is provided with electrodes 5| and 52 adjacent to the surfaces'43 and 41 respectively. As in the Fig. 1 arrangement the electrodes on the concave surfaces are connected through conductors 24', 24' to a terminal 3|, while the electrodes on the opposing surfaces are connected through conductors 26',25 toaterminal 32.

The Fig. 2 device further includes an ultrasonic-frequency signal generator 53, having an output circuit coupled to the input circuit of an amplifier and impedance-matching unit 54. The output circuit of the unit 54 is connected across the terminals 3 I, 32. 4

In considering the operation of the device illustrated in Fig. 2, it will be seen that this device comprises means, including the electrodes 48, 49 and 5|, 52 and the volume of the aforesaid acouscical medium extending from the concave surfaces 42 and 43 toward the focal region, for applying electrical energy to the dielectric material of the bodies 44 and 45 and for utilizing the resulting mechanical energy developed at the focal region. Thus an electrical oscillation of ultrasonic frequency generated in th generator 53 is coupled into the amplifier and impedancematching unit 54. In the'unit 54' this signal is amplified and passed through an impedancetran'sforming network of any suitable construction to match the output circuit of the amplifier to the electrical driving point impedance of the parallel-connected electroded transducer structures 44 and 45. The resulting electrical signals pass through the electrical-energy-translating location provided by the terminals 3|, 32 and the associated conductors, whereupon theelectrical energy is translated by the pairs of electrodes 48, 49 and 5|, 52 and thus applied to the bodies 44 and 45. Hence it appears that the generator 53,

the unit 54, the two pairs of electrodes, and the interconnecting conductors constitute means for applying electrical energy to the dielectric ma terlal. a

The dielectric material of the bodies 44 and 45 preferably is barium titanate material everywhere electrically polarized in substantially the direction normal to the concave surfaces 42 and 43. The electromechanically responsive properties of this material are effective to cause transducing from the ultrasonic-frequency electrical energy applied to the material to a mechanical deformation of the bodies 44 and 45 in a thickness 'mode of motion normal to the concave surfaces 42 and 43. The volume of fluid acoustical medium in contact with the surfaces translates this mechanical energy in the form of a series of acoustical wave fronts which are focused upon the region in the neighborhood of the pointll. In this manner a large part of the spherical area surrounding the focal region in the neighborhood of the point 4| is effective to radiate acoustical en ergy toward that focal region. In fact, a device has been made in which the point 4| is completely surrounded by a spherical radiating surface on the inside of a hollow sphere of titanate material, except that a small hole was leftin the walls of the sphereto permit the application of a conductive electrode to its inner surface.

However, the Fig. 2 arrangement has the advantage that it is easy to arrange for the continuous motion of an acoustical medium through the space between the two bodies 4 and 45. This may be done, for example, by means of circulating pumps or blowers, not shown, for moving the acoustical fluid medium past the region of the point 4| in a general direction normal to the plane of the drawing of Fig. 2. With the illustrated arrangement, then, the transducing bodies develop concentrated acoustical energy in the region of the focal point 4| upon the application of electrical energy at relatively low intensity from the units 53 and 54. There are numerous applications for such a concentrated acoustical field. Among these might be mentioned the breaking up into small particles 'of fiocculant masses suspended in an acoustical medium, the accelerated aging of spirituous beverages, and generally the acceleration of chemical reactions taking place in a fluid medium. If desired, a liquid medium easily may be treated in the apparatus of Fig. 2 to achieve violent cavitation in the liquid at the focal region. Accordingly, the volume of the acoustical medium in contact with the surfaces 42 and 43, and extending toward and embracing the focal region, constitutes means for utilizing the mechanical energy developed at the focal region as a result of the application of electrical energy to the dielectric material of the bodies 44 and 45.

It is feasible, using ceramic techniques, to form a body of, electromechanically responsive material, for example, the body l2 in Fig. 1 or the bodies 44 and 45 in Fig. 2, having a concave focusof such a resonant frequency, so that the gener-,

ator 53 and the amplifier unit 54, togetherwith the associated terminals and wiring, constitute means coupled to the electrodes 48, 49 and 52 for providing electrical energy at an ultrasonic frequency in the neighborhood of a frequency exciting a mechanical thickness-mode resonance in the bodies 44 and 45. Purely by way of example, it may be mentioned that ceramic bowls such as the body I2 in the Fig. l arrangement and the bodies 44 and 45 in the Fig. 2 arrangement may be made of barium titanate material using commercially practical methods in thicknesses within the range of 0.3 to 0.1 inch. The fundamental thickness resonance frequency for these thicknesses is approximately 0.3 to 1.0 megacycle per second, respectively.

Fig. 3 illustrates in block form apparatus suitable for the production of relatively stable suspensions or dispersions of fine solids in a liquid. The fine solids may have particle dimensions somewhat greater than those of colloidal particles, so that settling tends to occur. However, it has been found that in many cases treatment of the liquid containing the fine solids with ultrasonic acoustical energy very substantially prolongs the time required for settling. Referring to the block diagram, liquid in a storage tank BI and a finely divided solid contained in a storage vessel 62 as a powder or thick slurry are fed through suitable metering devices or valves 63 and 64 respectively to an agitator vessel 66. In the vessel 66 a conventional agitator screw or propeller, not illustrated, maintains the solids in a temporary state of roughly uniform distribution throughout the body of the liquid in the vessel 66. The bottom of the vessel 66 may open directly into a small conduit which passes vertically through an ultrasonic treatment device 61 and out the bottom of that device. As this vertical conduit leaves the device 61 it may be provided with a valve 68, so that the setting of the valve 68 determines the rate of liquid flow through the conduit in the ultrasonic treatment device and hence the level of the liquid in the agitator vessel 96. An ultrasonic-frequency electrical signal source 69 has an output circuit coupled to 'a pair of terminals 3|, "to provide an electrical-energy-translating location at these terminals. Electrical connections from these terminals to electrodes in the device 61 are provided. The device 61, including the vertical conduit mentioned above and the electroded structure, will be described hereinbelow. Treated liquid containing the fine solid, which is now in a state of thorough dispersion throughout the liquid, passes through the valve 68 to a dispersion storage tank I I.

The ultrasonic treatment device is illustrated in axial cross section in the perspective view of Fig. 4. The conduit mentioned hereina'bove appears in section at 1'2, and is provided at its lower end with the butterfly valve 88. The conduit 12 may be of a rubber material. The treatment device consists essentially of a closed, hollow, cylindrical body-13 of circular lateral cross section. The body 13 is maintained in a coaxial disposition relative to the conduit 12 by means of a bottom closure in the form of a disk 14 of any suitable material impervious to a liquid medium 16 which almost fills the cylindrical body 13. The disk 14 has a centralhole throughwhich the conduit 12 passes and is cemented to the outsidesmfaceof V.

cave inner surface 11 of the boclv 13 to and through the walls of the conduit 12 may be, for example, water or castor oil. Electrodes 18 and 19 are provided, individually disposed adjacent to the concave inner surface 11 and to the outer surface of the hollow cylindrical body 13. These electrodes are connected to the electrical terminal means 3 l, 32 as in the other embodiments discussed hereinabove.

The conduit 12 in the Fig. 4 arrangement defines a mechanical-energy-translating location determined by the concave inner surface 11 of the hollow cylindrical body 13 and coinciding with an axially extensive focal region in the neighborhood of the axis of that cylindrical body. The electromechanically responsive material of the body 13 is electrically polarized to provide the desired major electromechanical response of the material of the cylindrical body, this response involving radial motion of the concave inner surface 11. Thus, when electrical energy at an ultrasonic frequency is applied from the source 69 and translated through the electrical-energytranslating location including the terminals 3|, 32 to the dielectric material of the body 13, the electromechanical response of this material produces a radial motion of the electroded inner surface 11 with resultant propagation of acoustical energy to the walls of the conduit 12. At any instant the acoustical wave front passing through the walls of the conduit is in phase at all parts of the conduit, resulting in the developing of concentrated acoustical energy in the liquid contained within the conduit 12. This concentrated acoustical energy causes mechanical work to be done upon the liquid within the conduit, or at least causes powerful and remarkably thorough mechanical agitation of the contents of the conduit, resulting in a highly effective dispersion action, whereby mechanical energy developed at the axially extensive focal region within the conduit is utilized to obtain the desired thorough dispersion of the fine solid material in the liquid from the tank 6 I.

Referring now to Fig. 5. there is shown in a partly sectionalized perspective view a focused electromechanical devicecomprising another body 8| of electromechanically responsive polycrystalline dielectric material having a concave major surface approximately coinciding with a substantial portion of a hypothetical cylindrical surface, determining a mechanical-energy-translating location coinciding with an axially extensive focal region in the neighborhood of the axis of the cylindrical surface. While the concave major surface 11 of the-Fig. 4 arrangement is a closed cylindrical surface, the body 8| of the Fig. 5 arrangement is formed in the shape of a trough.

The concave inner surface 82 of the trough coincides approximately with a major portion of a hypothetical cylindrical surface but not with an entire closed cylindrical surface. The upper portions of the cylinder, for example the upper of the circular section of the cylinder, are-removed at the top of the trough to permit the introduction of objects to be treated in the focal region extending axially of the trough. An electrode 83 is formed adjacent to the concave surface 82, while an electrode 84 is disposed adjacent to the outer surface of the cylindrical trough.

The electrodes 88 and 84 are connected to the respective terminals II and 32. The trough is filled or partly fllled'with a liquid acoustical medium 88. The liquid 88 is retained in the trough by walls 81 securely fastened to the ends of the trough.

To provide for the motion of objects to be treated through the liquid 88 in the trough an overhead conveyor track '88 is disposed directly above the center of the trough. Suspended from the track 88 and movable therealong are a large number of evenly spaced hooks 89, from which may be suspended a corresponding number of objects 8| to be treated. For convenience of illustration only a few of the hooks 88 and objects 9| suspended therefrom are shown in Fig. 5. The track 88 dips down toward the surface of the liquid 88 at one end of the trough and bends up away from that surface at the other end of the trough, so that the objects 9| are suspended in the focal region in the neighborhood of'the axis of the trough during most of their passage along the trough.

During the operation of the Fig. 5 arrangement, a source of electrical signals is coupled to the. terminals 8|, 32 as in the arrangement of Figs. 3

and 4. The resulting motion of the concave inner wall of the trough 8| causes a concentration of acousto-mechanical energy in the axial region of the trough, where the objects 9| are suspended in the acoustical medium 86. The objects 9| may be any objects which it is desired to subject to the acoustical energy. For example, these objects may be thin shells or molds filled with a thermosetting liquid or plastic material. The acoustical energy concentratedin the axial region of the trough not only causes the material molds, an operation which heretofore might have,

required stacking the filled molds in thermostatically controlled ovens for periods of many hours. It also has been observed that treatment such as is afforded by the Fig. 5 device may be used to ac-' celerate the formation of a gel from suitable liquid material in the molds. Numerous other applications of the devices of the type described will be apparent to those familiar with tse extraordinary results which can be obtained by the use of ultrasonic or other acoustical fields.

In the'Fig. 5 device the quantity of the liquid 8 may adjusted so that the liquid level just reaches the axis of the cylindrical trough. If the hooks 88 then are shortened, so that the bottom surfaces of the objects 9| are immersed to only a smalldepth in the liquid, the acoustical energy is transmitted to the upper parts of the objects 8| through the materials of the objects themselves rather than through the liquid to all surfaces of the objects. This prevents excessive local effects hich might occur withinthe totally immersed objects '9I at restricted regions therewithin at which the acoustical energy from the body 8I is focused.

In the arrangements described he einabove a focal region is provided in the neighborhood of the center of curvature of a spherical surface or in the neighborhood of the axis of a-cylindrical surface. In many cases it-is' practical to arrange 14 for the application or utilization of the mechanical energy directly at such a focal region. However, in other cases it is more convenient to apply or utilize the mechanical energy, converted toor from acoustical energy propagating in generally parallel or collimated paths, in an elongated location which is not itself a focal region relative to an electromechanically sensitive body. This end may be accomplished by means of suitable refracting or reflecting apparatus designed for operation with acoustical energy.

Fig. 6 illustrates a focused electromechanical device comprising a body IOI of electromechanically responsive polycrystalline dielectric material having a spherical shape, similar to the bodies I2, 44, and 45 illustrated in the arrangements of Figs. 1 and 2. The body l0l in Fig. 6 is provided with electrodes I02 and I03 adjacent respectively to the concave and to the convex major surfaces of the body. The electrodes I03 and I02 are connected respectively to terminals 3| and 32, establishing an electrical-energy-translating location in the device. The Fig. 6 arrangement is v placed in a closed container or tank I04 holding a suitable liquid medium I06, so that a volume of the liquid I06 serves as an acoustical medium in effective acoustical contact with the electrode I02 on the concave surface and extending toward the focal region in the neighborhood of the center of curvature of the concave spherical surface.

The device illustrated in Fig. 6 also includes m ans. dispos d near this focal region in effective acoustical contact with the medium I05 and including a surface I01 effective to change the curvature of an acoustical wave front, for converting between acoustical energy which propagates in non-parallel paths in the regions between the concave electroded surface I02 and the lastmentioned means including surface I01 and related acoustical energy which propagates in generally parallel paths in an elongated mechanicalene gy-translatin'z location within a tube I08.

While the device illustrated in Fig. 6 may be used in such a manner that mechanical energy, applied to a liquid I09 inside the tube I08, takes the form of acoustical energy having substantial components propagating as a beam along the tube I09 toward and through the surface I01 and thence to the concave surface of the body IN, the operation of the device will be described for the more usual case of propagation of acoustical energy in the other direction, that is, from the body IOI toward the focal region and thence through ,the surface I01 for collimation into generally parallel paths propagating in the liqu d I09 away from the body IOI. For operation in the latter manner any suitable source of ultrasonic-frequency electrical signal energy is coupled to the terminals 3|, 32, as in the arrangements of Figs. 2-5.

In the Fig. 6 device the surface I01 is a curved surface of a thin sheet of material such as aluminum, disposed between the body IOI and the focal point of its concave major surface so asto be near the focal region in the neighborhood of that focal point.' The purpose of the thin sheet having a surface I0! is merely to establish the shape of the interface between two different acoustical conductors, so that any thin. impervious, and incompressible sheet of the desired shape may beused in contact with the medium I06 and separating it from the different acoustical medium I09. The liquid I06 may be. for example, c loroform or carbon tetrachloride, having a velocity of propagation of acoustical energy 15 roughly two-thirds of that of water or castor oil. When the liquid I09 is wateror other material hayinga relatively high velocity of propagation of acoustical energy, the arrangement including the curved surface I01 in conjunction with the two liquids I06 and I09 in contact therewith forms an acoustical refracting means, which in the illustrated acoustical system performs the function of a collimating lens. Of course, if the liquids I06 and I09 did not have substantially different acoustical properties, this refracting means would have to be a lens-shaped body of a solid or liquid material having a different acoustical property so as to provide refraction at its surfaces. One end of the tube I08 is fitted around the edges of the surface I01. The liquid I09, which is to be treated, may be introduced at the other end of the tube I08, and the tube is provided with an exit pipe II I leading to storage facilities, not shown, outside of the tank I04.

The operation of the Fig. 6 device now will be described, electrical energy being applied from any suitable source to the electrodes I02 and I03 to cause the translation of roughly spherical wave fronts of acoustical energy through the liquid I06 toward the focal region of the device. This resultant propagation of acoustical energy from the concave surface I02 through the acoustical medium I06 to the curved surface IN is such as to eifect collimation at that surface of the acoustical energy into generally parallel paths in the elongated acoustical-energy-translating region furnished by the liquid I09 in the tube I08. Thus the refracting means causes collimated acoustical energy to propagate relatively to the curved surface I01 through an elongated mechanical-energy-translating location, remote from the concave surface I02, in the tube I08. This tube may be any elongated vessel, disposed with the longitudinal direction thereof in approximate alignment with the direction of the aforesaid generally parallel paths and with one of the ends of the vessel facing the curved surface I'I of the acoustical refracting means. The tube I08 is effective for delimiting an elongated region of small cross-sectional area relative to the area of the concave surface I02. Within this region the energy generated at the large surface I02 may be concentrated for absorption by a body of liquid which could not absorb mechanically the desired amounts of acoustical energy in a reasonable time if all the liquid had to be treated at the focal region of the device. As an example, it may be desired to degas the liquid I09 which passes through the tube I08 and pipe III in the direction of the arrows. The acoustical excitation of the liquid I09 in tube I08 then causes violent bubbling with removal of the gas, which escapes through the open end of the tube I03. The liquid I08 and the arrangements for circulating it through the tube I08 constitute means for utilizing the resulting mechanical energy developed in the elongated acoustical-energy-translating region within the tube. A collimating arrangement of the type shown in Fig. 6 with a long, openended vessel such as the tube I08 is particularly useful when the mechanical utilization of the acoustical energy is so rapid or violent that the utilization of the available energy in a relatively small focal region would be impractical.

Fig. 7 illustrates an alternative arrangement including a curved reflecting surface I2I ofthin material such as aluminum. A body of water I22 fills the space between a roughly hemispherical body I23 and the acoustical mirror I2 I. The body I23 is fitted into a container I24. The mirror I2I rests against the back of the container I24 with an air space between the mirror and the container, so that an acoustical impedance mismatch exists at the mirror I2I which discourages transmission of acoustical energy into the space behind the mirror. The remaining interior surfaces of the container I24 are covered with a. layer I26 of glass wool or other acoustical absorbent material to prevent undesirable reflections. The hemispherical body I23 has a central opening into which a rubber plug or window I2! is fitted. The outside surface of the plug I21 is in contact with an aqueous liquid I09 in a tube I08 having entranc and exit ducts.

In operation, electrical energy may be supplied to the dielectric material of the body I23 by any suitable means, not shown in this figure. This causes acoustical energy to radiate from the spherical inner surface of the body I23 toward the central point I29 of that surface. Before reaching the point I29, however, the acoustical energy is reflected into a parallel beam, which passes upward through the plug I21 and into the tube I08, where it is utilized to treat the liquid I09 as in the Fig. 6 arrangement.

While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A focused electromechanical device for transducing between two types of energy, one type of which is mechanical energy in an acoustical medium at a focal region of said device and the other type of which is electrical energy translated by electrodes thereof, comprising: a body of electromechanically responsive polycrystalline dielectric material having a concave major surface, determining a mechanical-energy-translating location at a focal region in front of said concave surface, and electrically polarized to provide a major electromechanical response in a thickness mode of motion normal to said concave surface; electrode means, includin electrodes individually disposed adjacent to said concave surface and to the opposing surface of said body, and including electrical terminal means coupled to said electrodes to establish an electrical-energytranslating location; and means for applying energy of one of said two types to the corresponding one of said energy-translating locations and for utilizing energy of the other of said types developed at the other of said energy-translating locations.

2. A focused electromechanical device for transd-uoing between two types of energy, one type of which is mechanical energy in an acoustical medium at a focal region of said device and the other type of which is electrical energy translated by electrodes thereof, comprising: a body of electromechanically responsive polycrystalline dielectric material having a concave major surface, determining a mechanical-energy-transla-ting location at a focal region in front of said concave surface, and electrically polarized to provide a major electromechanical response in a thickness mode of motion normal to said concave surface; electrode means, including electrodes individually disposed adjacent to said conone of said two types to the corresponding one of said energy-translating locations and for utilizing energy of the other of said types developed at the other of said energy-translating locations.

3. A focused electromechanical device for transducing from mechanical energy in an acoustical medium at a focal region of said device to electrical energy translated by electrodes thereof comprising: a body of electromechanically responsive polycrystalline dielectric material having a concave major surface, determining a focal region in front of said concave major surface, and electrically polarized to provide a major electromechanical response in a thickness mode of motion normal to said concave surface; electrodes individually disposed adjacent to said concave surface and to the opposing surface of said body; a volume of an acoustical medium in ef-. fective acoustical contact with said concave surface and extending toward said focal region; means for applying mechanical energy to said focal region to effect acoustical propagation of said mechanical energy through said volume of said acoustical medium to said concave surface of said dielectric body; and means including said electrodes for utilizing the resulting electrical energy developed in said dielectric material.

4. A focused electromechanical device for the transducing from electrical energy, translated by electrodes associated with said device, to mechanical energy in an acoustical medium at a focal region of said device comprising: a body of electromechanically responsive polycrystalline dielectric material having a concave major surface, determining a focal region in front of said concave surface, and electrically polarized to provide a major electromechanical response in a thickness mode of motion normal to said concave surface; electrodes individually disposed adjacent to said concave surface and to the opposing surface of said body; a volume of an acoustical medium in effective acoustical contact with said concave surface and extending toward saidfocal region; and means, including said electrodes and said volume of said acoustical medium, for applying electrical energy to said dielectric material and for utilizing the resulting mechanical energy developed at said focal region.

5. A focused electromechanical device for transducing between two types of energy, one type of which is mechanical energy in an acoustical medium at a focal region of said device and the other type of which is electrical energy translated by electrodes thereof, comprising:.,a body of electromechanically responsive polycrystalline titanate material having a concave major surface, determining a mechanical-energytranslating location at a focal region in front of said concave surface, and electrically polarized to provide a major electromechanical response in a thickness mode of motion normal to said concave surface; electrode means, including electrodes individually disposed adjacent to said concave surface and to the opposing surface of said pplying energy of one of said two types to the corresponding one of said energy-translating locations and for utilizing energy of the other of said types developed at the other of said ener ytranslating locations.

6. A focused electromechanical device for transducing between two types of energy, one type of which is mechanical energ in an acoustical medium at a focal region of said device and the other type of which is electrical energy translated by electrodes thereof, comprising: a :body of polycrystalline dielectric material composed primarily of barium titanate having a concave major surface, determining a mechanical-energy translating locationat a focal region in front of said concave surface, and electrically polarized to provide a major electromechanical response in a thickness mode of motion normal to said concave surface; electrode means, including electrodes individually disposed adjacent to said concave surface and to the opposing surface of said body, and including electrical terminal means coupled to said electrodes to establish an electrical-energy-translating location; and means for apply energy of one of said two types to the corresponding one of said energy-translating locations and for utilizing energy of the other of said types developed at the other of said energytranslating locations.

7. A focused electromechanical device for transducing between .two types of energy, one type of which is mechanical energy in an acoustical medium at a focal region of said device and the other type of which is electrical energy translaced by electrodes thereof, comprising: a hollow cyclindrical body of electromechanically responsive polycrystalline dielectric material having a concave inner surface, determining a mechanical-energy-translating location coinciding with an axially extension focal region in the neighborhood of the axis of said cylindrical body, and electrically polarized to provide a major electromechanical response of said material of said cylindrical body involving radial motion of said concave inner surface; electrode means, including electrodes individually disposed adjacent to said concave inner surface and to the outer surface of said hollow cylindrical body, and including electrical terminal means coupled to said electrodes to establish an electrical-energy-translating location; and means for applying energy of one of said two types to the corresponding one of said energy-translating locations and for utilizing energy of the other of said types developed at the other of said energy-translating locations.

8. A focused electromechanical device for transducing between two types of energy, one type of which is mechanical energy in an acoustical medium at a focal region of said device and the other type of which is electrical energy translated by electrodes thereof, comprising: a body of electromechanically responsive polycrystalline dielectric material having a concave major surface approximately coinciding with a substantial portion of a hypothetical cylindrical surface, determining a mechanical-energy-translating location coinciding with an axially extensive focal region in the neighborhood of the axis of said cylindrical surface, and electrically polarized to provide a major electromechanical response in a thickness mode of motion normal to said concave surface electrode means, including electrodes individually disposed adjacent to said concave surface and to the'opposing surface of said body, and including electrical terminal means coupled to said electrodes to establish an electrical-energy-translating location; and means for applying energy of one of said two types to the corresponding one of said energy-translating locations and for utilizing energy of the other of said types developed at the other of said energy-translating locations.

9. A focused electromechanical device for transducing between two types of energy, one type of which is mechanical energy in an acoustical medium at a focal region of said device and the other type of which is electrical energy translated by electrodes thereof, comprising: a body of electromechanically responsive polycrystalline dielectric material having a concave major surface approximately coinciding with a substantial portion of a hypothetical spherical surface, determining a mechanical-energy-translating location coinciding with a focal region in the neighborhood of the center of said spherical surface, and electrically polarized to provide a major electromechanical response in a thickness mode of motion normal to said concave surface; electrode means, including electrodes individually disposed adjacent to said concave surface and to the opposing surface of said body, and including electrical terminal means coupled to said electrodes to establish an electrical-energy-translating location; and means for applying energy of one of said two types to the corresponding one of said energy-translating locations and for utilizing energy of the other of said types developed at the other of said energy-translating locations.

10. A focused electromechanical device for transducing between two types of energy, one type of which is mechanical energy in an acoustical medium at a focal region of said device and the other type of which is electrical energy translated by electrodes thereof, comprising: a body of electromechanically responsive polycrystalline dielectric material having a concave major surface, determining a mechanical-energy-translating location at a focal region in front of said concave surface, having a, generally uniform thickness between said concave surface and the opposing surface of said body in directions normal to said concave surface, and everywhere electricaly polarized in substantially said normal directions to provide a major electro-mechanical response in a thickness mode of motion; electrode means, including electrodes individually disposed adjacent to said concave surface and to said opposing surface of said body, and including electrical terminal means coupled to said electrodes to establish an electrical-energy-translating location; and means for applying energy of one of said two types to the corresponding one of said energy-translating locations and. for utilizing energy of the other of said types developed at the other of said energy-translating locations.

11. A focused electromechanical device for transducing between two types of energy. one type of which is mechanical energy in an acoustical medium at a focal region of said device and the other type of which is electrical energy translated by electrodes thereof comprising: a body of electromechanically responsive polycrystalline dielectric material having a concave major surface, determining a mechanical-energy-translating location at a focal region in front of said concave surface, having a generally uniform thickness between said concave surface and the opposing surface of said body in directions normal to said concave surface, and everywhere electrically polarized in substantially said normal dimotions to provide a major electro-mechanical 20 response in a thickness mode of motion; electrode means, including electrodes individually disposed adjacent to said concave surface and to said opposing surface of said body, and including electrical terminal means coupled to said electrodes to establish an electrical-energy-translating location; and means for applying energy of one of said two types to the corresponding one of said energy-translating locations at a frequency in the neighborhood of a frequency exciting a mechanical resonance determined by said thickness of said body and for utilizing energy of the other of said types developed at the other of said energy-translating locations.

12. A focused electromechanical device for transducing from electrical energy, translated by electrodes associated with said device, to mechanical energy in an acoustical medium at a focal region of said device comprising: a body of electromechanically responsive polycrystalline dielectric material having a concave major surface, determining a focal region in front of said concave surface, and electrically polarized to provide a major electromechanical response in a thickness mode of motion normal to said concave surface; electrodes individually disposed adjacent to said concave surface and to the opposing surface of said body; a volume of an acoustical medium in effective acoustical contact with said concave surface and extending toward said focal region; and means, including means coupled to said electrodes for providing electrical energy at an ultrasonic frequency in the neighborhood of a frequency exciting a-mechanical thickness-mode resonance in said body and including said volume of said acoustical medium, for applying electrical energy to said electroded dielectric material and for utilizing the resulting mechanical energy developed at said focal region.

13. A focused electromechanical device for transducing between two types of energy, one type of which is mechanical energy in an acoustical medium at a focal region of said device and the other type of which is electrical energy translated by electrodes thereof, comprising: a body of electromechanically responsive polycrystalline dielectric material having a concave major surface, determining a focal region in front of said concave surface, and electrically polarized to provide a major electromechanical response in a thickness mode of motion normal to said concave surface; electrode means, including electrodes individually disposed adjacent to said concave surface and to the opposing surface of said body, and including electrical terminal means coupled to said electrodes to establish an electricalenergy-translating location; a volume of an acoustical medium in effective acoustical contact with said concave surface and extending toward said focal region; means, disposed near said focal region in effective acoustical contact with said medium and including a surface effective to change the curvature of an acoustical wave front, for converting between acoustical energy which propagates in non-parallel paths in the regions between said concave surface and said lastmentioned means and related acoustical energy which propagates in generally parallel paths in an elongated mechanical-energy-translating location; and means for app ying energy of one of said two types to the corresponding one of said energy-translating locations and for utilizing energy of the other of said types developed at the other of said energy-translating locations.

.- 14. A focused electromechanical device for transducing between two types of energy, one type of which is mechanical energy in an acoustical medium at a focal region of said device and the other type of which is electrical energy translated by electrodes thereof, comprising: a body of electromechanically responsive polycrystalline dielectric material having a concave major surface, determining a focal region in front of said concave surface, and electrically polarized to provide a major electromechanical response in a thickness mode of motion normal to said con-.- cave surface; electrode means, including electrodes individually disposed adjacent to said concave surface and to the opposing surface of said body, and including electrical terminal means coupled to said electrodes to establish an electrical-energy-translating location; a volume of an acoustical medium in efiective acoustical contact with said concave surface and extending toward said focal region; acoustical refracting means, including a curved surface disposed near said focal region in effective acoustical contact with said first-mentioned medium and separating said medium from a different acoustical medium, for converting between acoustical energy which propagates in non-parallel paths in the regions between said first-mentioned concave surface and said curved surface and related acoustical energy which propagates, relatively to said curved surface, in generally parallel paths through an elongated mechanical-energy-translating location remote from said concave surface; and means for applying energy of one of said two types to the, correspondingone of said energy-translating locations and for utilizing energy of the other of said types developed at the other of said energytranslating locations.

15. A focused electromechanical device for transducing between two types of energy, one type of which is mechanical energy in an acoustical medium at a focal region of said device and the other type of which is electrical energy translated by electrodes thereof, comprising: a body of electromechanically responsive polycrystalline dielectric material having a concave major surface approximately coinciding with a substantial portion of a hypothetical spherical surface, determining a focal region in the neighborhood of the center of said spherical surface, and electrically polarized to provide a major electromechanical response in a thickness mode of motion normal to said concave surface; electrode means, including electrodes individually disposed adjacent to said concave surface and to the-opposing surface of said body, and including electrical terminal means coupled to said electrodes to establish an electrical-energy-translating location; 9. volume of an acoustical medium in effective acoustical contact with said concave surface and extending toward said focal region; means, disposed near said focal region in effective acoustical contact with said medium and including a surface effective to change the curvature of an acoustical wave front, for converting between acoustical energy which propagates in non-parallel paths in the regions between said concave surface and said last-mentioned means and related acoustical energy which propagates in generally parallel paths in an elongated mechanical-energy-translating location; and means for applying energy of one of said two types to the corresponding one of said energy-translating locations and for utilizing energy of the other of said types developed at the other of said energy-translating locations.

16. A focused electromechanical device for transducing between two types of energy, one

type of which is mechanical energy in an acoustical medium at a focal region of said device and.

the other type of which is electrical energy translated by electrodes thereof, comprising: a body of electromechanically responsive polycrystalline dielectric material having a concave major surface approximately coinciding with a substantial portion of a hypothetical spherical surface, determining a focal region in the neighborhood of the center of said spherical surface, and electrically polarized to provide a major electromechanical response in a thickness mode of motion normal to said, concave surface; electrode means, including electrodes individually disposed adjacent to said concave surface and to the opposing surface of said body, and including electrical terminal means coupled to said electrodes to establish an electrical-energy-translating location; a volume of an acoustical medium in effective acoustical contact with said concave surface and extending toward said focal region; means, disposed near said focal region in eifective acoustical contact with said medium and including a curved surface eifective'to change the curvature of an acoustical wave front, for converting between acoustical energy which propagates in non-parallel paths in the regions between said concave surface and said last-mentioned means and related acoustical energy which propagates in generally parallel paths in an elongated region of small crosssectional area relative to the area of said concave surface; an elongated vessel, disposed with the longitudinal-direction thereof in approximate alignment with the direction of said generally parallel paths and with one of the ends thereof facing said curved surface of said last-mentioned means, for delimiting said region of small crosssectional area to define in said vessel an elongated mechanical-energy-translatin location; and means for applying energy of one of said two types to the corresponding one of said energy. translating locations and for utilizing energy of the other of said types developed at the other of said energy-translating locations.

17. A focused electromechanical device for transducing from electrical energy, translated by electrodes associated with said device, to mechanical energy translated through an acoustical medium toward a focal region of said device comprising: a body of electromechanically responsive polycrystalline dielectric material having a concave major surface, determining a, focal region in front of said concave surface, and electrically polarized to provide a major electromechanical response in a thickness mode of motion normal to said concave surface; electrodes individually disposed adjacent to said concave surface and to the opposing surface of said body; a volume of an acoustical medium in effective acoustical contact with said concave surface and extending toward said focal region; means, disposed near said focal region in effective acoustical contact with said medium and including a curved surface effective to change the curvature of an acoustical wave front, for converting between acoustical energy which propagates in non-parallel paths from said first-mentioned concave surface to said curved surface and related acoustical energy which propamentioned energy into generally parallel paths in said elongated region, and for utilizing the resulting mechanical energy developed in said elongated acoustical-energy-translating region.

18. A focused electromechanical device for transducing between two types of energy, one type of which is mechanical energy in anacoustical medium at a focal region of said device and the other type of which is electrical energy translated by electrodes thereof, comprising: a body of titanate-type electromechanically responsive polycrystalline material having a concave major surface, determining a mechanical-energy-translating location at a focal region in front of said concave surface, and electrically polarized in directions differing at various portions of said body and everywhere substantially normal to said concave surface thereof; electrodes individually disposed adjacent to said concave surface and to the opposing surface of said body and constituting an electrical-energy-trans1ating location; and means for applying energy of one of said two types to the corresponding one of said energytranslatlng locations and for utilizing energy of the other of said types developed at the other of said energy-translating locations.

19. A focused electromechanical device for transducing between two types of energy, one type of which is mechanical energy in an acoustical medium at a focal region of said device and the other type of which is electrical energy translated by electrodes thereof, comprising: a body of titanate-type electromechanically responsive polycrystalline material having a concave major surface, determining a mechanical-energy-translating location at a focal region in front of said concave surface, and electrically polarized in directions differing at various portions of said body and everywhere substantially normal to said concave surface thereof; electrodes individually disposed adjacent to said concave surface and to the opposing surface of said body and constituting an electrical-energy-translating location; and means, including an acoustical medium embracing said focal region and in effective acoustical contact with said concave surface, for applying energy of one of said two types to the corresponding one of said energy-translating locations and for utilizing energy of the other of said types developed at the other of said energy-translatin locations.

ALFRED L. W. WILLIAMS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,447,061 Franklin Aug. 17, 1948 2,486,560 Gray Nov. 1, 1949 2,503,831 Mason Apr. 11, 1950 FOREIGN PATENTS Number Country Date 654,673 Germany Dec. 24, 1937 572577 Great Britain Jan. 11, 1946 OTHER REFERENCES Ser. No. 337,106, John, Jr., et al. (A. P. 0.), published May-18, 1943. 

